This invention relates generally to an antenna, particularly an broadband dual-frequency tablet antenna.
In the structure of a generic dipole antenna in xc2xdxcex (wavelength) shown in FIG. 1, the distance between a positive and a negative pole is theoretically the shorter the better in obtaining efficacy of signal transmission and reception.
Some conventional tablet dipole antennas are shown in FIGS. 2 and 3. In FIG. 2, the antenna is constructed by disposing a linear positive pole (signal end) 51 on a baseplate 50 and cambered negative poles by sides (earth end) 52, in which the positive and the negative poles 51, 52 are connected with the core 54 and the woven shield 55 of a coaxial cable 53, respectively. The antenna shown in FIG. 3 is constructed by assembling and disposing a linear positive pole (signal end) 61 on the back side and a piece of copper foil as a negative pole (earth end) 62 on the front side of a baseplate 60, in which the positive and the negative pole 61, 62 are connected with the core 64 and the metallic woven shield 65 of a coaxial cable 63, respectively.
The effective bandwidth of the conventional tablet antennas, which is defined as the quotient of an applicable band width divided by a center frequency, is about 5.0xcx9c10.0% limited to the xc2xcxcex portion. Taking the frequency band of 2.4xcx9c2.5 GHz for instance, the signal bandwidth is only 100xcx9c240 MHz that limits the applicable range of the tablet antenna to a single frequency band, which is considered already out-of-date in catching the time pulses.
This invention is a broadband dual-frequency tablet antenna, comprising a set of dipole antennas, a baseplate, and an inductive investing-piece, in which the pole-set of the antennas disposed on the baseplate is composed of cambered narrow straps in length of xc2xcxcex (wavelength) of a low-frequency band and spaced out in a distance of xc2xcxcex of the center frequency in a high-frequency band. The entire dipole antenna construction and baseplate is thoroughly invested with an inductive investing piece.
The primary objective of this invention is to provide a set of dipole antennas for signal transmission and reception in a low-frequency band, and space out the antenna pole-set a xc2xcxcex (wavelength) of a high-frequency band, such that a high-frequency harmonic oscillation will be brought about in response to that of a low-frequency band to thereby achieve the purpose for dual-frequency transmission and reception.
Another objective of this invention is to widen the bandwidth by adjusting: the cambered shape of the poles, the width of the narrow strap, the interval between the narrow straps, and using the inductance of the inductive investing-piece properly to increase the effective bandwidth to reach as high as 18% of the frequency band and thereby to obtain the efficacy of a broadband dual-frequency tablet antenna.
Yet another objective of this invention is to provide a broadband dual-frequency tablet antenna, in which a set of low-frequency poles is spaced out about xc2xcxcex (wavelength) of a high-frequency band to therefore extend the antenna only by a length less than xc2xcxcex of the high-frequency band.
For more detailed information regarding advantages or features of this invention, at least an example of preferred embodiment will be fully described below with reference to the annexed drawings.